(1) Field of the Invention
The invention relates to gas turbine engine components, and more particularly to an anti-rotation lock for preventing relative movement between two such components.
(2) Description of the Related Art
A gas turbine engine includes one or more forward compressor sections for increasing the pressure of an incoming air stream. Each compressor section includes alternating axial stages of rotating, rotor blades and stationary, stator vanes disposed within a casing structure. The stator vanes are supported by outer shrouds or by inner and outer shrouds. The outer shrouds include a pair of circumferentially extending rails for use in assembly with the casing structure. Multiple stator vanes may be manufactured as a single module, referred to as a stator segment. Stator segments are less expensive to manufacture and allow less air leakage than individual stator vanes.
To simplify assembly with the rotor blades, the casing structure is typically split axially into two or more arcuate sectors, referred to as a split case. Circumferential grooves, within the internal periphery of the split case, accept the circumferential rails of the stator segment. A thickened flange is located radially outward from the split case for joining the split case with fasteners during assembly. The thickened flanges are referred to as split flanges.
During assembly, each stator segment is inserted into the split case by engaging the stator segment rails with the corresponding circumferential grooves in the case. Each stator segment is guided into the grooves in turn, until all of the stator segments are loaded. The split case is next fit around a pre-assembled rotor and joined by fasteners at the split flanges.
During normal operation of the gas turbine engine, temperature variations between the split case and the stator segments necessitate a suitable cold-clearance gap between adjacent stator segments. Also, aerodynamic loading of each stator segment generates a tangential force approaching five hundred pounds. In order to uniformly distribute the cold-clearance gaps and prevent circumferential sliding of the stator segments in the split case grooves, anti-rotation locks must be utilized for each stator segment.
The requirement for an anti-rotation lock is particularly important at the locations adjacent to the split flanges. If the stator segments rotate circumferentially in the split case grooves and bridge the split flange after assembly, disassembly of the compressor may be difficult or even impossible. Because the split flanges are thicker than the remainder of the split case, contain a plurality of fasteners and are a source of air leakage, an unconventional anti-rotation lock is required at this location.
Anti-rotation locks of the type described in U.S. Pat. No. 6,537,022 to Housley, et al., are effective in areas of a split case where the locks do not interfere with any external casing features, such as fasteners. In the area of the split flange; however, the fasteners attaching the case sectors preclude their use. Anti-rotation locks as described in U.S. Pat. App. 2003/0082051 to Bertrand, et al., although effective, require precise machining of the split case grooves and stator segments and are susceptible to vibratory wear. Each of the above locks may contribute to increased engine weight and air leakage, which are important considerations as well.
What is needed is an anti-rotation lock for use at a split flange that does not interfere with external casing features, does not require extensive machining, is not susceptible to vibration and has minimal impact on engine weight and air leakage.